The present invention concerns signal-light systems, most especially those provided along roads and highways. It is known to provide emergency-phone stations at intervals along the length of a highway, the emergency-phone stations being distributed along the length of a communications cable laid along the length of such highway. Such emergency-phone stations may be provided with signal-light systems. For example, each emergency-phone station in a series of such stations may be provided with a lamp which, from a remote central station, is caused to blink, to warn drivers that they are approaching the site of an accident, or the like. An operator at the remote central station selects which emergency-phone stations are to have their respective lamps blink, and the power needed to effect blinking of the lamps is transmitted to the activated emergency-phone stations via a power-supply line which runs along the communications cable and which supplies operating power to electrical equipment at such emergency-phone stations.
The German periodical "ADAC-Motorwelt," Nov. 1976, pp. 30-32, disclosed the use of the emergency-phone stations provided at intervals along the length of a highway for the generation of an optical warning action informing drivers of upcoming hazards. The optical warning action in question was to be implemented by blinking the exterior lamp with which each such emergency-phone station was anyway provided.
In order to increase the perceivability of the blinking action, Federal Republic of Germany published allowed patent application DE-AS No. 19 33 436 disclosed the use not of the exterior lamp anyway provided at such stations, but instead the provision of each such station with an electronic flash lamp capable of being flashed at higher brightness levels. Because the flash power needed by such flash lamps is greatly in excess of the power transmittable along the power line of the phone stations' communication cable, it is necessary to provide each station with a storage condensor, serving to periodically accumulate an amount of stored energy adequate to implement a flash.
Even when such storage capacitors are used, so as to be able to furnish to the flash lamps an instantaneous flash power vastly in excess of the power level instantaneously transmittable along the available cable, the fact remains that the low level of transmittable power places severe limits upon the amounts of flash energy which can be accumulated during the interflash intervals, especially when one considers that the interflash intervals must be kept quite short, in order that the flashing action attract the attention of drivers moving past the flashing stations at highway speed. For example, in the system disclosed in the aforementioned DE-AS No. 19 33 436, each emergency-phone station is provided not only with storage-capacitor circuitry, but additionally with signal-evaluating circuitry needed for the reception and evaluation of signals transmitted along the available cable for identification of which stations are to have their lamps flash. Such signal-evaluating circuitry consumes electrical power which might otherwise be used for flash energy, in a context where available energy is at a minimum.